In telecommunication, a new technology called LTE-U (Long Term Evolution in Unlicensed) is being developed, where an LTE system can be applied to other frequencies than previously standardised in 3GPP (3rd Generation Partnership Project) standards.
3GPP is working to finalize release 13 LTE LAA (Licence Assisted Access) standard based on LTE-U. The LTE LAA system will require listen before talk functionality prior a transmission. The 3GPP standard version release 14 will include duplex operation, where both transmission and reception will occur at the unlicensed frequency band. For instance, LTE-U can be deployed to use the 5 GHz band, which is currently used mostly for WiFi. LTE-U can be used to deploy LTE as Supplemental Downlink (SDL), with the PCell (Primary Cell) always operating on a carrier in a licensed band.
In such an environment, listen before talk (LBT) is utilised to reduce the risk of transmitters from different (or the same) radio access technologies transmitting on the same radio channel at the same time. However, the LBT procedure is sometimes inefficient in terms of throughput.